Various suspension systems for supporting equipment in aerial locations are known. Such systems are particularly important in the making of motion pictures, where cinematographic equipment has to be suspended at high elevations to capture panoramic views. A boom mounted on a vehicle may give the necessary height, or it may be possible to use the roof of a nearby building. However, systems which are not ground-based are increasingly being used, i.e. systems that use cables or similar means for suspension. U.S. Pat. No. 4,710,819, granted to Garrett W. Brown on Dec. 1, 1987, discloses one such system. It uses at least three flexible members, such as cables, to suspend an equipment support member inside of a support structure. Each of the flexible members extends around a pulley on the support structure, and has one end connected to the equipment support member and the other end connected to a motor assembly controlled by a computer. The relative movement of the flexible members is synchronized by the computer, and this arrangement allows a computer operator to control the position of the support member within the support structure. A somewhat similar concept for directing an underwater exploration device is disclosed in U.S. Pat. No. 3,324,239, granted to I. C. Jacobson on Jun. 6, 1967.
Numerous difficulties have been found to exist with the suspension system of Brown. A major problem is stress on the cables; because of the angles involved, supporting an item weighing several hundred pounds may create a tension in the cables many times higher; the cables have been known to break under such stress. Brown's three-cable and four-cable systems incorporate no redundancy; if a cable breaks, the supported item freely falls. A related problem with the Brown system is the stress placed on the motor assemblies to which the tables connect. The motors are under continual pressure to maintain tension on the cables, which leads to their frequent burn out. Another serious problem that has been experienced with the Brown system is creation of wave motion in the Cables; this results in serious problems for cinematographers and others who require a highly stable camera platform with smooth movement.
The aerial support platform mechanism of the subject invention has a redundancy built into its cable system; if a support cable should break, a parallel drive cable takes on the support cable load and prevents the supported item from falling. Because the vertical cables in the subject invention only have to carry the weight of the supported item and are not part Of the overall suspension system as in the Brown system, those cables can be made considerably thinner than is possible with Brown's system. That allows the vertical cables supporting a camera on a first platform member of the invention to be invisible to a second camera on a second platform member, even if the separation between the two is only a few feet. Because the motors of the subject platform mechanism only act to move carriages and not to support cables as in Brown, the motors have little or no burn out. The cables of the subject platform mechanism experience negligible wave motion because the start/stop portion of the software that controls movement has a built-in inertia compensation, similar to that found in modern elevator control systems.